Process for jacketing a core



July 19, 1960 G. A. LAST PROCESS FOR JACKETING A com:

. z y l3 JAMJUF Filed NOV. 13. 1956 5 I A i Geor do 25 i 8? PROCESS FOR JACKETING A CORE George A. Last, Bountiful, Utah, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Nov. 13, 1956, Ser. No. 621,973 1 Claim. (Cl. 29-422) This invention rel-ates to a process for enclosing a core in a metal jacket and, more particularly, to the use of pressure-welding in such a process.

It is known to be desirable to enclose in aluminum nuclear-fuel cores of natural uranium that are to be cooled by water in a neutronic reactor, because aluminum resists corrosion by water and has a low capacity for the absorption of neutrons. The difliculty is that the aluminum jacket for a fuel core may not possess a high degree of integrity as a corrosion barrier at regions where it has been soldered or fusion-welded. It is difficult to remove oxides completely from aluminum, and the presence of such oxides in soldered or welded joints in aluminum jackets makes them porous.

According to the present invention, a method of enclosing a core in an aluminum jacket has been devised which involves welding in such a way that oxides are pushed to one side and kept out of the weld. Thus the weld is not porous and constitutes a good corrosion barrier.

In the drawings:

Fig. 1 is a sectional view of a core to be enclosed;

Fig. 2 is a sectional view of a cup in which the core is to be enclosed;

Fig. 3 is a sectional view showing the cup being drawn on the core;

Fig. 4 is a sectional view showing the drawn cup and core positioned in a forging die that is to close the cup over the core;

Fig. 5 is a sectional view showing the cup, core, and forging die after the cup has been closed over the core; and

Fig. 6 is a fragmentary sectional view similar to Fig. 1, of a modification in which the core is of soft metal and a hard metal disk is provided on top of the core.

In Fig. l a core 10 which may be of natural uranium or uranium containing U to the extent of 1.75% enriched uranium has one end 11 somewhat roughened by rough machining and a central recess 12 which is located on the end 11 and has about the same diameter and depth. The peripheral portion of the end 11 is rounded as indicated at 13. In Fig. 2 a cup 14 of 28 aluminum has an internal diameter about the same as the diameter of the core 10 and is somewhat shorter than the core 10.

As shown in Fig. 3, the core 10 is positioned in the cup 14, and the cup is drawn through a die 15 by a plunger 16 applied against the end 11 of the core 10 so as to be thinned and to become firmly seated on the core 10. As shown in Fig. 4, the drawing operation elongates the cup 14 until it is longer than the core 10 and has at its open end a cylindrical wall 17 which is radially inwardly thickened and locks the core 10 in the cup 14 by extending over the rounded peripheral portion 13 of the end 11 of the core 10. The wall 17 is radially thickened, because the plunger 16 has a smaller diameter than the core 10.

Before the core 10 is inserted in the cup is annealed at 400 C. for minutes, degreased, and

7 14, the cup 0 had an external diameter Patented July 19, 1960 deoxidized. The core 10 is degreased, pickled in nitric acid, rinsed in water, rinsed in an organic solvent such as acetone or alcohol, and dried in air. If the core 10 is to be mechanically bonded to the cup 14 in the drawing operation, the core is electrochemically roughened in a manner known to those skilled in the art before the above operations of degreasing, pickling, etc. Before the drawing die 15 is applied to the cup 14, a wax-type lubricant is applied to the exterior of the cup, care being taken that neither the slug nor the interior of the cup be contaminated with the lubricant.

Now before the wall 17 is processed as shown in Figs. 4 and 5, the interior of the wall 17 is wire-brushed for breaking up of the aluminum oxides. The cup 14 and core 10 are placed in a stationary die 18 which closely fits the sides of the cup 14 and includes a removable plug 10 supporting the bottom of the cup 14. The interior of the die 13 is coated with a wax-type lubricant to a level not above the open end of the cup 14, so that the interior of the cup wall 17 will not be contaminated with the lubricant. Now a movable die or punch 19a which fits the interior of the stationary die 18 and has an axial hole 20 narrower at the bottom than at other regions is applied with great pressure against the end of the cylindrical wall 17. As a result of this operation the wall 17, i.e., flows radially inwardly to the axis of the core 10 while being reduced in length, until, as shown in Fig. 5, the metal of the wall 17 flows together and welds at the axis of the core 10, forming an end closure 21 with a short internal projection 22 in the core recess 12 and a long external projection 23 extruded out through the axial hole 20 in the movable die 19. The canning or enclosing of the core 10 is now complete except for machining to desired finished dimensions including removal of the external projection 23, so that the core 10 is now in a complete aluminum jacket 24 of which the end closure 21, pressure-welded at the axis of the core, forms a part.

It will be understood, of course, that the volume of the wall 17 is a little greater than that of the end closure 21. It is important that the height of the wall 17 be not too great relative to its radial thickness so that the wall 17 will not buckle during the upsetting operation. It is also important that the axial weld of the end closure 21 be kept as free as possible of aluminum oxides so that the weld will not be porous. The roughening of the end 11 ot the core 10 as previously described, the formation of the internal projection 22 in the core recess 12, and the extrusion of the external projection 23 through the die hole 20 prevents the accumulation of oxides at the region of the weld of the end closure 21.

The drawing of the cup 14 shown in Fig. 3 and the upsetting and welding of the wall 17 into the end closure 21 shown in Fig. 5 is carried out at room temperature. These operations can be carried out to encase cores of metals other than uranium. The main requisite is that the core not flow at room temperature and at the pressure required to make the aluminum flow as described. If the core were as soft as aluminum, the core might be extruded outwardly through the die hole 20 and thus not be completely encased.

By way of example, a core 10 having a diameter of 1.336", a length of 4.01 inches and an axial recess .125" in depth and .125 in diameter, was inserted in a cup 14, having a length of 3.150", a base thickness of .185, an internal diameter of 1.346", an external diameter of 1.750", and a section tapering for 1.10" of the length of the cup to an external diameter of 1.53 inches at the base of the cup.

After processing by the drawing die 15, the cup 14 of 1.558 and the wall 17 was 0.8" in height and 0.2" in radial thickness. The diameter of the die opening 20 was .25 at the bottom and .375" thereabove, and the projection 23 extruded therethrough was 3" in length. A load of 150 tons was ap- "It it is -desired'to encase a soft metal, a. hard-metal inseft 25 is' applied, as shown in Fig". 6, to the end of a sbft-metal core'26'over which the cup 14 is to be closed. The insert 25 prevents the core 26 from being extruded through the die hole 20. The insert 25 has an axial recess 27 which has the same purposeas the core recess 12, namely, to receive the internal projection 22 which carries oxides out of the Weld region. The upper side of the insert 25 is roughened like the end 11 of the core 10 and the peripheral portion is rounded like the portion 13 of the core 10; The example cited in the-two preceding paragraphs was followed except that the core was 3.81" length and. the insert 25 was .2" in thickness.

It is'also understood that the invention is not to be limited by the details given herein but that it may be modified within the scope of the appended claim.

What is claimed is:

In a process for closing the open end of a cup-shaped aluminum jacket projecting beyond one end of a cylindrical uranium-containing core snugly fitted in the jacket,

plied to the'movable die to produce the end closnre by the steps of forcing the said open end of the jacket radially inwardly over the said one end of the core perpendicularly to theaxis thereof and welding to one another the portions of the open end of the jacket meeting at the axis of the core; the combination with said last step, of the step of Working and axially displacing the said meeting portions simultaneously in opposite directions to form an external projection of small diameter on the axis of the core and an internal projection of small diameter entering a small axial recess in the said one end of the core.

References Cited in the file of this patent UNITED STATES PATENTS 268,687 Kautmann Dec. 5, 1882 2,309,360 Southwell Jan. 26, 1943 2,567,012 Ddnelan Sept. 4, 1951 2,697,954 sewter Dec. 28, 1954 2,791,483 Foxon Feb. 8, 1955 2,761,207 Dodd Sept. 4, 1956 2,873,238 Ohlinger Feb. 10, 1959 FOREIGN PATENTS 218,656 Great Britain Sept. 10, 1925 

